This invention relates to an electrical connector having at least an elastically deformable spring contact and, in particular, to an electrical connector which is interposed between a printed circuit board and an electronic part and which electrically connects the printed circuit board and the electronic part by applying compressive force from the outside. Since the electronic part referred to in the specification includes the printed circuit board, this invention is also directed to a connector which electrically connects two printed circuit boards.
Referring to FIGS. 1, 2, and 3A to 3D, three existing connectors will be described hereafter.
At the outset, a first existing electrical connector will be described referring to FIG. 1.
In FIG. 1, a spring contact 10 is fixed to an insulator 20 at a central portion thereof. The spring contact 10 has a round contact projection 18 at a bending top and a second contact region 19 at a lower end thereof, respectively. The spring contact 10 is located at an initial position depicted by a solid line in a natural condition where no external force is applied. In this condition, the round contact projection 18 is located at a position remotest from the surface of the insulator 20, that is, a position on a two-dot chain line extending in parallel to the surface of the insulator 20.
When an electronic part (not shown) is made to approach the surface of the insulator 20 in a connecting direction perpendicular thereto, the contact pad of the electronic part touches the round contact projection 18. As a result, the spring contact 10 is elastically deformed to move from the initial position to a deformed position depicted by a two-dot chain line.
Following the movement of the spring contact 10 from the initial position (solid line) to the deformed position (two-dot chain line), the round contact projection 18 slides on the lower surface of the electronic part over a certain distance. In other words, the lower surface of the electronic part is wiped by the round contact projection over the certain distance. Such distance is represented by D1 in the figure and will be referred to as a wiping amount of the spring contact 10.
Next referring to FIG. 2, a second existing electrical connector will be described.
The second existing electrical connector is similar to the first existing electrical connector except that the radius of curvature of the bending top of the spring contact 10 is greater than that of the first existing electrical connector.
With this structure, the round contact projection 18 is brought into contact with the contact pad of the electronic part over a wide area as compared with the first existing electrical connector. Therefore, the spring contact 10 of the second existing electrical connector has a wiping amount D2 smaller than the wiping amount D1 of that of the first existing electrical connector. It is noted here that, in case where the contact force between the contact pad of the electronic part and the round contact projection 18 of the spring contact 10 in the second existing electrical connector is equal to that in the first existing electrical connector, the contact force per unit area of a contact portion is weaker in the second existing electrical connector than in the first existing electrical connector.
Turning to FIGS. 3A to 3D, a third existing electrical connector will be described. This connector is described in Japanese Unexamined Patent Publication (JP-A) No. 73960/1997.
Each of a plurality of U-shaped spring contacts 220 comprises a metallic plate which is formed into a generally U shape by punching and bending. The U-shaped spring contact 220 has a round contact projection 221 formed at its bending top. The U-shaped spring contact 220 has at its one end a slightly curved portion toward the inside of the U shape, with a second contact region 222 formed at the slightly curved portion. The U-shaped spring contact 220 has the other end 223 wider than the remaining portion of the U-shaped spring contact 220 so that the U-shaped spring contact 220 is prevented from slipping out or disengaged from a corresponding one of a plurality of contact receiving holes 211 formed in the insulator 20. Between the bending top and the second contact region 222, the U-shaped spring contact 220 is provided with a first bending portion 224 bent outwards of the U shape and a second bending portion 225 bent towards the inside of the U shape. Further, the U-shaped spring contact 220 has, between the bending top and the other end 223, a third bending portion 226 bent towards the inside of the U shape.
As shown in FIG. 3B, the plurality of contact receiving holes 211 are separated from each other by a plurality of partition walls 212 each of which is shorter than the plate thickness of the insulator 20 provided with the contact receiving holes 211. Therefore, a clearance 213 is formed between the lower end of each of the partition walls 212 and the upper surface of a printed circuit board 90. Each of the contact receiving holes 211 is a through-hole formed in the insulator 20 into which the U-shaped spring contact 220 is inserted. The contact receiving hole 211 has a rectangular section and extends generally perpendicular to the surface of the insulator 20. The contact receiving hole 211 has an upper portion widened toward its upper end so that the width A at the upper end is greater than the width B of a lower portion.
Referring to FIG. 3A, a gap between two opposite legs of each of the U-shaped spring contacts 220 is greatest at a gap C between the second bending portion 225 and the other end 223. The U-shaped spring contact 220 is formed so that the gap C is greater than the width B (FIG. 3B) of the lower portion of the contact receiving hole 211.
As shown in FIG. 3B, when the U-shaped spring contacts 220 is inserted into the contact receiving hole 211 formed in the insulator 20, the second bending portion 225 and the other end 223 are compressed and tightly held in the lower portion of the contact receiving hole 211 because the gap C of the contact 220 is greater than the width B of the lower portion of the contact receiving hole 211. At this time, the second contact region 222 of the U-shaped spring contact 220 is displaced from a position P (FIG. 3A) on the upper surface of the printed circuit board 90 to a position Q (FIG. 3B) slightly shifted leftwards. It is noted here that the position P is offset leftward from a position R where a perpendicular line from the round contact projection 221 of the U-shaped spring contact 220 intersects the upper surface of the printed circuit board 90.
Referring to FIG. 3C, each of the U-shaped spring contacts 220 is compressed between the lower surface of an electronic component 100 and the upper surface of the printed circuit board 90 to be elastically deformed. Referring to FIG. 3D, electrical connection between the electronic component 100 and the printed circuit board 90 has been completed. During elastic deformation, the second contact region 222 of the U-shaped spring contact 220 is further displaced leftward along the upper surface of the printed circuit board 90 from the position Q to a position S (FIG. 3C) slightly offset leftward and finally to a position T slightly offset leftward again.
In the first existing electrical connector, the round contact projection formed at the bending top of the spring contact is greatly displaced in the direction perpendicular to the connecting direction. Therefore, when the contact pad of the electronic part is small, the round contact projection of the spring contact may possibly be failed to touch the contact pad of the electronic part.
In the second existing electrical connector, the radius of curvature of the bending top of the spring contact is greater than that of the first existing electrical connector so that the displacement in the direction perpendicular to the connecting direction is small. However, the contact force between the round contact projection of the spring contact and the contact pad of the electronic part per unit area is weak.
In the third existing electrical connector, the first and the second bending portions are present between the first and the second contact regions of the spring contact. Consequently, the inductance of the connector is great.